• State
  • Locked Locked
  • Replies 4 replies
  • Subscribers 31 subscribers
  • Views 3751 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DRV8825 standby connection causes stepper motor to overheat

Kirit patel1
Prodigy 80 points
Other Parts Discussed in Thread: DRV8825

My DRV8825 based controller design involves using a 1.2A NEMA 17 Stepper motor continuously rotating at about 150 rpm. The design is in production and occasionally a stepper motor overheats soon after the continuous stream of pulses is stopped. The 12V DC power supply for the Motor is rated at 1.5A. As long as the motor is running (hours at a time), the DVM reads 11.92VDC at the input of DRV8825, and both the motor and the DRV8825 are cool to the touch;  however, the moment the step pulses are stopped, the DVM reads 11.35 VDC, indicating the DRV8825 is demanding more standby current from the power supply than can be supplied and, of course, the stopped motor starts to overheat. DRV8825 never gets hot, nSLEEP is always disabled, ENABLE is always active, microstepping is always active, DECAY is left unconnected, and the GND pad under the DRV8825 chip properly soldered to the 2-layer PCB. H..E..L..P!

  • 0
    TI__Guru** 114905 points

    Hi Kirit,

    Do you have access to a current probe? Can you check to see if one of the windings is not being regulated properly.

    If that is the case, can you try setting DECAY pin to high (fast decay)? There will be more current ripple, but it will help us debug the problem.

    Thank you.

     

  • 0 in reply to Rick Duncan
    TI__Expert 8885 points

    Kirit,

    DRV8825 comes with fixed blanking time of 3.75usec. There is high probability that while motor is at halt, current regulation is lost due to minimum on-pulse width. You can verify it by measuring the voltage and current across motor windings.

    If above is true, the only way to resolve the issue is to reduce the motor current either by reducing the voltage (which is hardly possible) or insert  additional series resistance to reduce the motor current.

     Best Regards

    Milan- Motor Application Team

  • 0 in reply to Milan Rajne
    TI__Expert 8885 points

    Kirit,

    I would like to make a correction in my previous post, in which I mentioned that the only way to resolve the issue is to reduce the motor current either by reducing voltage or adding additional resistance. 

    As Rick has suggested in his post, setting decay pin to fast decay mode would also help if current regulation is lost at halt condition.

     Best Regards

    Milan

  • 0 in reply to Milan Rajne
    Prodigy 80 points

    Thank you, Rick, and Milan, for the feedback.

    I got off to a tangent with no luck finding a  current probe..so took  me a while to reply.

    I pulled-up DECAY (with a 4.7K Ohm Res to 5V), but it did not make any noticeable difference.

    Fortunately, I have access to multiple motors, multiple DRV8825 Controllers, and multiple power supplies. Here were additional experiments:

    1. Changed 2-3 motors, same Controller, same PwrSupp, DECAY pulled-up: Each motor getting noticeably hot when not running (i.e., no STEP PULSES from the micro). 12VDC at the PWRSupp output read 11.5 to 11.65 VDC

    2. Same as above, except that in case, steady STEP pulses for the motor to run at 158 rpm: None of the motor would get hot even after several minutes of wait. In each case, DVM read the PwrSupp output around 11.9x VDC.

    3. Tried Different Controller, and different Power Supply; DECAY floating; Motor got hot when not running (PwrSupp output 11.6VDC) and not hot when running (PwrSupp output 11.9 VDC). Basically, change of Power Supply or a Second controller did not make any difference.

    4. All of the motors above came from one mfg. So, next, tried a different mfg.'s motor: Same Controller, same PwrSupp, DECAY pulled-up high, no STEP pulses: After several minutes, new motor still remains cool to touch, although PwrSupp output does read 11.6 VDC. Subsequently, ran this motor at 158 rpm: runs cool, but the PwrSupp output still remains around 11.6 VDC!

    Next step is to try a differensource of t (more heavy duty ) power supply. Will update you again.